The present invention relates generally to the transport of sample fluids into a mass spectrometer. More particularly, the invention relates to devices and methods that use a flexible fluid-transporting assembly to deliver sample fluids from a well plate through a mass spectrometer interface directly into an inlet opening of a mass spectrometer.
Mass spectrometry is an important analytical technique for the identification of chemical or biochemical compounds. By ionizing sample molecules and sorting the ionized molecules according to their mass-to-charge ratios, mass spectrometry has demonstrated its usefulness in the identification of a wide variety of molecules, such as small organic compounds synthesized in large libraries, biological compounds, such as peptides, proteins, and carbohydrates, and a wide variety of naturally occurring compounds. For example, mass spectrometry may employ electrospray technology that allows ions to be produced from a sample fluid containing sample molecules in a carrier liquid. Typically, electrospray technology produces an ionized aerosol by passing a sample fluid through a rigid capillary extending in a horizontal direction and subjecting the outlet terminus of the capillary to an electric field. The electric field is usually generated by placing a source of electrical potential, e.g., an electrode, near the outlet terminus of the capillary, wherein the electrode is held at a voltage potential difference with respect to the outlet terminus. As the sample fluid exits the capillary from the outlet terminus, droplets having a net charge are formed. When the carrier liquid is evaporated from the droplets, ionized sample molecules are produced. In some instances, a plurality of capillaries may be employed to deliver ions from multiple sample fluids to a mass spectrometer. See, e.g., U.S. Pat. No. 6,191,418 to Hindsgaul et al. The ionized sample molecules are then sorted in a vacuum according to mass-to-charge ratio. When all sample molecules carry the same charge, e.g., are singly charged, sorting the ionized sample molecules according to mass-to-charge ratio is equivalent to sorting the sample molecules according to mass.
Microfluidic devices have also been proposed for use to carry out chemical analysis and processing. Their small size allows for the analysis and processing of minute quantities of a sample fluid, which is an advantage when the sample is expensive or difficult to obtain. See, e.g, U.S. Pat. No. 5,500,071 to Kaltenbach et al., U.S. Pat. No. 5,571,410 to Swedberg et al., and U.S. Pat. No. 5,645,702 to Witt et al. Typically, microfluidic devices are formed from substantially planar structures comprised of glass, silicon, or other rigid materials and employed in conjunction with internal or external motive means to move fluids therein for analysis and/or processing. Microfluidic devices represent a potentially inexpensive or disposable means that integrates sample preparation, separation, and detection functionality in a single tool. In addition, microfluidic devices are well suited to process and/or analyze small quantities of sample fluids with little or no sample waste.
A number of patents and applications have described the incorporation of electrospray technology in microfluidic devices. For example, U.S. Pat. No. 5,994,694 to Tai et al. describes a micromachined electrospray nozzle for mass spectrometry. Instead of using a glass capillary to delivery sample fluid for electrospray ionization, an overhanging silicon nitride microchannel serves as an electrospray ionization nozzle. The microchannel is located within a rigid silicon support substrate.
In addition, commonly owned U.S. Ser. No. 09/324,344 (xe2x80x9cMiniaturized Device for Sample Processing and Mass Spectroscopic Detection of Liquid Phase Samplesxe2x80x9d), inventors Yin, Chakel, and Swedberg (claiming priority to Provisional Patent Application No. 60/089,033), describes a miniaturized device for sample processing and mass spectroscopic detection of liquid phase samples. The described device comprises a substrate having a feature on a surface in combination with a cover plate. Together, a protrusion on the substrate and a corresponding protrusion on the cover plate may form an on-device mass spectrometer delivery means. On-device features such as microchannels and apertures may be formed through laser ablation or other techniques. Other commonly owned applications include: U.S. Ser. No. 09/711,804, which describes a similar microfluidic device having a protruding electrospray emitter; and U.S. Ser. No. 09/820,321, which describes a microfluidic device that includes a means for nebulizing a sample fluid from an outlet of the microfluidic device for delivery into an ionization chamber.
There is a current need in the pharmaceutical industry to quickly screen, identify, and/or process a large number and/or variety of samples. For instance, the samples may represent a collection or library of organic and/or biological compounds. Such compounds may originate from a number of sources and may be, for example, extracted from naturally occurring plants and animals or synthesized as a result of combinatorial techniques. In particular, there is a need to screen biological compounds, such as peptides, proteins, and carbohydrates. Thus, microfluidic devices may contain multiplexed features of multiple inlets and multiple spray tips. For example, U.S. Pat. No. 6,245,227 to Moon et al. describes an integrated monolithic microfabricated electrospray nozzle and liquid chromatography system. This patent also proposes that an array of multiple systems may be fabricated in a single monolithic chip for rapid sequential fluid processing and generation of electrospray for subsequent analysis.
Well plates are often used to store a large number of samples for screening and/or processing. Well plates are typically single piece items that comprise a plurality of wells, wherein each well is adapted to contain a sample fluid. Each well of the well plate has a small interior volume, defined in part by an interior surface extending downwardly from an opening at an upper surface of the well plate. Such well plates are commercially available in standardized sizes and may contain, for example, 96, 384, or 1536 wells per well plate.
To bring these samples from their containers to the mass spectrometer, with or without intermediate processing is currently a cumbersome task, requiring excessive fluid volume and time. Pipettes are typically employed to convey sample fluid from the wells of a well plate into an inlet of an analytical and/or processing device. While robotic and/or automated systems using pipette technology may be configured to handle a large number of sample fluids, pipettes suffer from a number of intrinsic drawbacks. For example, pipettes are incapable of performing continuous fluid transfer from a well to the inlet. In addition, many pipettes are typically incapable of dispensing fluids in a horizontal direction into an analytical and/or processing device. Thus, there is a need for a fluid-transporting device that overcomes the drawbacks of pipettes.
Although microfluidic devices often comprise motive means that are well suited for effecting controlled fluid flow, such devices are generally unsuitable for transporting sample fluids directly from a sample well to a mass spectrometer. As discussed above, most microfluidic devices are made from glass, silicon, or other rigid structures. While it is possible to place such devices directly over a well plate in an attempt to transport fluids directly from the sample well for processing before introduction into a mass spectrometer, typical microfluidic device construction would require the device to be positioned vertically on its edge, which would adversely affect control over fluid flow. In addition, when electrospray nozzles are an integral part of a rigid microfluidic device, it may be difficult to achieve the proper alignment needed to carry out mass spectrometry. That is, the relative positions of the well plate, microfluidic device, and a mass spectrometer inlet have to be precisely and appropriately situated to rapidly and efficiently perform mass spectrometric analysis for a plurality of sample fluids.
Thus, there is a need in the art to improve sample transport from a well plate into mass spectrometric devices and, optionally, to exploit the motive means and functionality associated with microfluidic devices. Furthermore, there is a need to provide a means to overcome the inherent alignment problems associated with rigid microfluidic devices for use in mass spectrometry.
In a first embodiment, the invention relates to a device for transporting sample fluids to a mass spectrometer. The device comprises a well plate, a fluid transporting assembly, and a mass spectrometer interface. The well plate is comprised of a plurality of wells, wherein each well is defined by an interior surface extending downwardly from an opening at an upper surface of the well plate. The fluid-transporting assembly is comprised of a plurality of fluid-transporting conduits, each extending from an inlet port to an outlet port, wherein the assembly exhibits sufficient flexibility to allow movable positioning of the outlet ports with respect to the inlet ports. Each inlet port of the fluid-transporting assembly is positioned in fluid communication with a different well of the well plate to allow any sample fluid contained in the well to be transported upwardly through the well opening and into the inlet port. The mass spectrometer interface is provided in fluid communication with the outlet ports of the fluid-transporting assembly. As a result, a plurality of flow paths is formed, each flow path originating at a well and traveling in succession through the conduit inlet port, the conduit, the conduit outlet port, and the mass spectrometer interface. Fluids emerging from the mass spectrometer interface are then introduced into a mass spectrometer.
Typically, the fluid-transporting assembly is formed from a substrate and a cover plate arranged in fluid-tight relationship over the substrate surface, and the fluid-transporting conduits are each defined by a channel formed in the substrate surface in combination with the cover plate. The substrate, the cover plate, or both may be comprised of a polymeric material, preferably a biofouling-resistant material such as polyimide. Optionally, a plurality of processing chambers is also provided, wherein each chamber is in fluid communication with a conduit of the fluid-transporting assembly to allow sample fluid processing to take place therein after a sample fluid exits a well and before the sample fluid enters the mass spectrometer interface.
In addition, the mass spectrometer interface may be constructed according to a desired function. Thus, the interface may comprise one or more electrospray nozzles. In such a case, the interface typically comprises an electrically conductive material. For example, a metallization layer may be provided on an interior and/or exterior surface of the mass spectrometer interface. In addition, the mass spectrometer interface may be formed as a discrete component that is attached to the fluid-transporting assembly, or formed as an integral portion of the fluid-transporting assembly.
In order to transport fluid from the wells and through the fluid transporting assembly, the inventive device may further include a motive means to transport sample fluid from each well upwardly through the fluid-transporting conduit in fluid communication therewith. In some instances, the motive means may comprise applying a voltage differential to induce electrokinetic flow. In addition or in the alternative, the motive means may comprise pressurizing at least one of the wells of the well plate.
Thus, in another embodiment, the invention relates to a mass spectrometric analytical device. The device comprises a well plate as described above, a fluid-transporting assembly, and a mass spectrometer interface. In addition, the fluid-transporting assembly comprises a substrate having a plurality of microchannels formed in a surface thereof, and a cover plate arranged in fluid-tight relationship over the substrate surface, wherein the cover plate and the microchannels together define a plurality of fluid-transporting conduits, each extending from an inlet port to an outlet port. Furthermore, a mass spectrometer inlet opening is provided in a fluid-receiving relationship to the mass spectrometer interface, which in turn, is in fluid communication with the outlet ports of the fluid-transporting assembly. Again, each inlet port of the fluid-transporting assembly is positioned in fluid communication with a different well of the well plate. As a result, a plurality of flow paths is formed, each flow path originating at a well and traveling in succession through the conduit inlet port, the conduit, the conduit outlet port, and the mass spectrometer interface. The fluid-transporting assembly is arranged such that the direction of the flow path from the wells to the fluid-transporting assembly differs from the direction of the flow path from the mass spectrometer interface to the mass spectrometer inlet opening.
In a further embodiment, the invention relates to a method for transporting a plurality of sample fluids to a mass spectrometer. The method involves: (a) providing a mass spectrometer interface and a fluid-transporting assembly that comprises a plurality of fluid-transporting conduits, each extending from an inlet port to an outlet port and exhibiting sufficient flexibility to allow movable positioning of the outlet port with respect to the inlet port, wherein at least one outlet port is in fluid communication with the mass spectrometer interface; (b) placing each inlet port of the fluid-transporting assembly in fluid communication with a different well of a well plate, wherein the well plate comprises a plurality of wells, each containing a sample fluid and further, wherein each well is defined by an interior surface extending downwardly from an opening at an upper surface of the well plate; (c) positioning the mass spectrometer interface to introduce a sample fluid from the well plate into an inlet port of a mass spectrometer; and (d) applying a motive force to transport a sample fluid from a selected well of the well plate through the opening of the selected well, the conduit in communication with the selected well, the mass spectrometer interface, and the inlet port of the mass spectrometer; wherein the direction in which the sample fluid is transported through the opening of the selected well is different from the direction in which the sample fluid is transported through the inlet port of the mass spectrometer.